Plasma reduction processing of materials

ABSTRACT

In a process for the reduction of a metalliferous ore or concentrate the ore or concentrate is first prepared into a particulate form. A reaction chamber ( 3, 103, 203, 301, 401, 503, 603, 702 ) is then charged with ore or concentrate, a reductant and an input gas. The reaction chamber ( 3, 103, 203, 301, 401, 503, 603, 702 ) is irradiated with electromagnetic radiation within a frequency range of  30  MHz to  300  GHz until a non-equilibrium plasma is initiated. The plasma is sustained and controlled with the radiation until the ore or concentrate is reduced to form reduction product.

FIELD OF THE INVENTION

[0001] The present invention relates to the chemical processing ofmaterials in a plasma environment, and in particular relates topyrometallurgical reduction processes in a plasma environment.

BACKGROUND OF THE INVENTION

[0002] The pyrometallurgical reduction of metalliferous ores andconcentrates typically involves the heating of the ore or concentrate ina smelting furnace with a reductant to a temperature which generallymelts the ore and at which chemical reaction of the ore/concentrate withthe reductant reduces the ore/concentrate into metallic product orhigher end-value product with a lower oxidation state. Large amounts ofenergy are required to initiate and sustain reduction processes in suchsmelting finances, and the recovery rate of metallic product oftenrenders such operations commercially unviable. The non-reducedcomponents of the ore/concentrate form a slag, which often containsvaluable metallic content. Recovery of the metallic content from suchslags is, however, again often commercially unfeasible by conventionalmethods.

[0003] Microwave radiation has been utilised in various industrialapplications for the application of energy to heat materials, includingthe microwave heating of chemical reactants to kinetically andthermodynamically stimulate the same for the initiation of chemicalreactions. Microwave treatment of metalliferous ores and othercomparable materials has been utilised as an augmentative precursortreatment, applying energy to the ore to thermodynamically stimulate thesame and prepare it for conventional recovery techniques such asconventional pyrometallurgical reduction, leaching or hydrometallurgicalrecovery processes.

OBJECT OF THE INVENTION

[0004] It is the object of the present invention to provide an improvedpyrometallurgical reduction process.

SUMMARY OF THE INVENTION

[0005] In a broad form the present invention provides a process for thereduction of a metalliferous ore or concentrate comprising the steps of:

[0006] preparing said ore or concentrate into a particulate form;

[0007] charging a reaction chamber with said ore or concentrate, areductant and an input gas;

[0008] irradiating said reaction chamber with electromagnetic radiationwithin a frequency range of 30 MHz to 300 GHz until a non-equilibriumplasma is initiated, and sustaining and controlling said non-equilibriumplasma with said radiation until said ore or concentrate is reduced toform reduction product.

[0009] Typically, pressure within said reaction chamber is maintainedbelow 300 kPa during irradiation thereof.

[0010] Typically, said pressure is also maintained above 40 kPa.

[0011] In several embodiments, said pressure is maintained at aboutatmospheric pressure.

[0012] Said plasma may be initiated in said input gas.

[0013] Alternatively or additionally, at least part of said input gasmay be decomposed during said irradiation, said plasma being initiatedat least in part in the decomposed product of said input gas.

[0014] The reductant will typically comprise a carbonaceous material.

[0015] The reductant may include a particulate carbonaceous materialblended with said ore or concentrate.

[0016] The reductant may include carbon monoxide gas, said input gasincluding said carbon monoxide gas, said plasma being initiated at leastin part in said carbon monoxide gas.

[0017] The reductant may comprise carbon monoxide gas and a particulatecarbonaceous material.

[0018] Alternatively, the reductant may comprise a reactive metal.

[0019] The input gas may include an inert gas.

[0020] The inert gas may comprise argon or nitrogen.

[0021] The input gas may comprise air.

[0022] The reductant may include methane.

[0023] Preferably, said radiation is microwave radiation.

[0024] The ore or concentrate may be a concentrate derived directly frommined ore.

[0025] Alternatively the ore or concentrate may be a non-ore derivedconcentrate. Said non-ore concentrate may be a residue derived, wastederived or mining derived concentrate, such as from mine tailings orconcentrator residue.

[0026] The ore or concentrate may be a concentrate in the form of aresidue, such as a slag, slurry or slime, derived from metallurgicalprocessing operations. Such residue may be derived frompyrometallurgical, hydrometallurgical, chemometallurgocal orelectrometallurigeal processing stages during primary, secondary and/ortertiary stages of metallurgical processing operations.

[0027] The reaction chamber may be in the form of a fluidised bedreactor.

[0028] The reaction chamber may alternatively be in the form of an oven,said ore or concentrate being charged into a crucible placed within saidoven.

[0029] The reaction chamber may be in the form of a rotary kiln reactor.

[0030] The reaction chamber may be in the form of a cyclone reactor.

[0031] The reaction chamber may be in the form of a conveyor fedreactor.

[0032] In such a conveyor fed reactor, said ore or concetrate ispreferably prepared into a pelletised particulate form.

[0033] Preferably, said reduction product is of metallic form.

[0034] Said metallic reaction product may be in the form of a fume, saidfume being extracted from said reaction chamber and separated from gasesproduced during said reduction.

[0035] Alternatively, said reduction product is a compound of reducedoxidation state.

[0036] The reduction product may be formed by reduction of said ore orconcentrate through a series of subsequent reduction reactions.

[0037] The process may include the step of generating carbon monoxide,said plasma being initiated and sustained at least in part in saidcarbon monoxide.

[0038] When said input gas includes air and said reductant includesparticulate carbonaceous material, said carbon monoxide may be generatedfrom reaction of oxygen within said air with said particulatecarbonaceous material.

[0039] Alternatively or additionally, when said reductant includesparticulate carbonaceous material, said carbon monoxide may be generatedfrom reaction of carbon dioxide produced during said reduction with saidparticulate carbonaceous material.

[0040] Alternatively or additionally, particulate carbonaceous materialmay be introduced into said reaction chamber after initiation of saidplasma, said carbon monoxide being generated from reaction of carbondioxide produced during said reduction, and/or oxygen within said airwhen said input gas includes air, with said introduced particulatecarbonaceous material.

[0041] Preferably, said ore or concentrate is enveloped in anon-oxidising or inert gas environment during said reduction and duringcooling of said reduction product following irradiation of said reactionchamber.

[0042] Preferably, said non-oxidising or inert gas is introduced to saidreaction chamber during said cooling.

[0043] In one embodiment, said input gas is passed through said ore orconcentrate during said irradiating step.

[0044] Preferably, said input gas is blasted upwardly through said oreor concentrate.

[0045] Preferably, said input gas is preheated prior to charging intosaid reaction chamber.

[0046] It has been a commonly held view that the generation of plasmasduring the microwave chemical processing of materials, and in particularduring the pyrometallurgical reduction of metalliferous ores andconcentrates, is detrimental to the process system hardware andmonitoring and control diagnostics equipment, and accordingly it istypical for such processes to be controlled in a manner to explicitlyavoid the generation of a plasma.

[0047] Reaction rates, however, can increase by one or more orders ofmagnitude under -plasma processing. A plasma is a mixture of excitedmolecules, atoms, ions, electrons and recombined particles in a groundstate host gas. With the high particle energies which are characteristicof such plasma components, the physical and chemical behaviour of thesecomponent particles differs markedly from equivalent particles in the“ground state”.

[0048] In pyrometallurgical processes conducted in a plasma environment,there is a predominance of reaction chemistry occurring at theplasma-solid or plasma-liquid interface. Whilst this feature ischaracteristic of pyrometallurgical processes in general, reaction ratesacross these interfaces are greatly enhanced by plasma chemistry, withan abundance of highly energised reactive species.

[0049] Plasmas initiated and sustained at “high” pressures exhibit anapproximate equivalence of temperature between electrons and heavyparticles (ions, atoms, excited molecules). Accordingly these plasmasare termed equilibrium plasmas, as there is (approximate) thermalequilibrium between particles. This is exhibited particularly at higherpressures as the high density of particles provides an increasedfrequency of collision between particles distributing energy relativelyevenly between particles, providing a consistent bulk temperaturethroughout the particle species of the plasma. Because of thehigh-energy densities (thermal mass), equilibrium plasmas have commonlybeen utilised as precursor methods in material processing for theircapability to heat, sinter, melt or vaporise solid materials. These areall essentially physical processes merely taking advantage of thephysical thermal kinetics (properties) of the equilibrium plasma.

[0050] Non-equilibrium plasmas, which are more characteristic of lowpressure environments, are characterised by particle temperaturenon-equivalence, with the “temperature” of electrons far exceeding thatof the temperatures of the heavier particles. FIG. 1 depicts theseparation of electron and heavy particle temperatures at low pressures,both with conventional plasmas and plasmas stimulated by microwave (orRF) radiation. It can be seen that at higher pressures, the electron andheavy particle temperatures merge. In a non-equilibrium plasma, thephysical and chemical behaviour of the component particles may beprofoundly different from that in the equivalent ground stateenvironment. In a non-equilibrium plasma, with the various particlespecies moving with different energies, the measure of such energy,typically in the form of a “temperature” will vary greatly betweenspecies and between particles in each species population. This isevident when “temperature”, a measure of thermal energy, is obtained bya mean reading by averaging-out the electron voltages (temperatureequivalents) of particles having no adjustment for “thermal mass”.Accordingly, the temperature of the plasma itself becomes meaningless asparticle “temperatures” vary by perhaps four orders of magnitude, and“bulls” temperature measurements of plasma by different methods candisagree by an order of magnitude.

[0051] The processing effectiveness of low pressure, non-equilibriumplasmas is imbued by the reactivity of the chemically active speciespresent rather than by the total energy available in the plasma Thisreactivity makes non-equilibrium plasmas more suited to systems reliantupon the chemical kinetics of the chemical reactions, as per that of thepresent application, than the equilibrium plasmas which have been usedprimarily in physical processes as discussed above.

[0052] The form of the diagram of FIG. 1 will be dependent upon variousparameters, including the gas composition, ionising characteristics ofthe species present, and the form of energy applied to the system togenerate the plasma. The pressure up to which a plasma will be of thenon-equilibrium form will thus vary depending on these and otherparameters.

[0053] Typical methods of producing plasmas are through ionisation byheating (thermal stimulation), ionisation by irradiation, and ionisingby electrical discharge. Whilst most plasma production methods willresult in an equilibrium plasma at pressures up to around atmosphericpressure, it is believed that the generation of a plasma by irradiation,particularly in the RF and microwave frequency ranges between 30 MHz and300 GHz, pushes the graph of FIG. 1 to the right as depicted, such thatnon-equilibrium plasmas can be generated and sustained at operationallyimportant pressures around atmospheric (101.4 kPa) and up to about threeatmospheres (about 300 kPa) under sufficient applied energy, appropriateavailable species (chemistry) and at responsive radiation frequencies.

[0054] This is believed to be as a result of the microwave radiationapplying energy to the dieletrically disparate particles of the plasma,in particular to the electrons. At frequencies within the RF andmicrowave frequencies, only the electrons in the ionised field canfollow the oscillations of the electric field applied. As a result theelectrons become more highly energised that the heavier particles of theplasma, such that the RF/microwave plasmas can generally be defined asnon-equilibrium plasmas. Such RF/microwave plasmas can be induced andoperated over a large pressure range, from below 0.1 kPa (for operationsoutside the main interest of the present invention), to pressures inexcess of 300 kPa

[0055] When a microwave field is applied across a gas, charged particlesin that gas are accelerated. Because the mass of electrons is much muchless than that of the heavier ion, atom and molecule particles, theaction of the field is primarily to give energy to the electrons.Accordingly, electron temperatures can be in the extremely high range oftens of thousands of kelvin whereas the apparent bulk temperature of theplasma (primarily determined by the heavier particles) is orders ofmagnitude lower.

[0056] Reaction rates are generally governed by the mass transportdiffusion of reactants, which is greatly enhanced by dielectric heatingmechanisms during RF/microwave processing, typically in the presence ofan RF/microwave stimulated plasma which, by definition, will have a highpopulation of reactive species.

[0057] Plasma processing utilising RF/microwave stimulation also enablesa great degree of control over the process, with the microwave radiationable to be directed to the reactant charge, in such a way as to envelopethe entire reactant charge within the reaction chamber or to occupy azone discretely within the charge. In continuous processing systems,residence time and thermochemical parameters can effectively becontrolled through control of the applied radiation, providing superiorprocessing or reduction results.

[0058] Whilst lower pressures well below atmospheric pressures ensuregeneration of an unambiguously non-equilibrium plasma with a largedisparity between the temperatures of the electron and heavierparticles, if the pressure in the reaction chamber is too low, then thedensity of reactive species to carry out the chemical processing will betoo low for economically viable processing. Accordingly, it is preferredthat the pressure of the reaction chamber in which the plasma isinitiated and sustained is greater than 40 kPa.

[0059] The inherent advantage of the non-equilibrium plasma chemistry(ionisation chemistry) of non-equilibrium plasmas when utilised inchemical and metallurgical applications is that these plasmas canprovide particles with the high energy required to stimulate andcomplete chemical reactions at high kinetic rates. For the range ofapplications relevant to the present application, high rates of masstransfer are desired with the high kinetic rate. Therefore, commerciallyviable productivity levels are often not achievable at extremely lowpressures which provide extremely low rates of mass transfer.

[0060] Conversely, the advantage of processing certain reactions undernon-equilibrium plasma conditions, despite low mass transfer rates, isthat in the low density plasma environment, the high energy freeelectrons and ionised particles experience a greatly increased mean freepath before collision and re-combination, imparting greatly increasedenergy to re-combination chemistry. This increased energy at possiblereaction sites enables the activation energy requirement to be met forreactions which require extremely high energy input to proceed.Consequently, certain thermodynamically demanding metallurgical andchemical reactions can be carried out efficiently, if slowly, or if atall, by utilising the extremely high energy particles at low pressures.

[0061] Processes which require protection from re-oxidation reactionsbenefit from the protection implied by removal of potential oxidationsources by initial and continuing evacuation of oxidising agents, suchas the common reduction reaction product carbon dioxide, from thereaction environment. This can be achieved by maintaining the process atlow pressures, continually evacuating the reaction chamber.Alternatively, or additionally, such carbon dioxide can be converted tothe reductant carbon monoxide with fine carbon in the reaction chamberat elevated temperatures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Preferred forms of the present invention will now be described byway of example with reference to the accompanying drawings wherein:

[0063]FIG. 1 is a diagram showing the separation of electron and heavyparticle temperatures in a plasma at varying pressures.

[0064]FIG. 2 is a partially cross sectioned view of a reaction chamberused in the process of Example 1.

[0065]FIG. 3 is a partially cross sectioned view of a reaction chamberused in the process of Example 2.

[0066]FIG. 4 is a partially cross sectioned view of a reaction chamberused in the process of Example 3.

[0067]FIG. 5(a) is a partially cross sectioned view of a reactionchamber used in the process of Example 4.

[0068]FIG. 5(b) is an enlarged fragmentary view of the top portion ofthe reaction chamber of FIG. 5(a).

[0069]FIG. 5(c) is a fragmentary cross sectional view of the gasgeneration system associated with the reaction chamber of FIG. 5(a).

[0070]FIG. 5(d) is a cross sectional view of the reaction chamber ofFIG. 5(a) taken through section 5-5.

[0071]FIG. 6 is a partially cross sectioned view of a reaction chamberused in the process of Example 5.

[0072]FIG. 7 is a partially cross sectioned view of a reaction chamberused in the process of Example 6.

[0073]FIG. 8 is a partially cross sectioned view of a reaction chamberused in the process of Example 7.

[0074]FIG. 9(a) is a cross sectioned view of a reaction chamber used inthe process of Example 8.

[0075]FIG. 9(b) is a cross sectional view of the reaction chamber ofFIG. 9(a) taken through section 9B-9B.

[0076]FIG. 9(c) is a cross sectional view of the reaction chamber ofFIG. 9(a) taken through section 9C-9C.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLE 1

[0077] This example details a process to reduce monazite [(Ce,La,Th)PO₄], using an incrucible batch reduction process, to eradicate thephosphorus (of the phosphate) and concentrate the reduced heavy metalsinto one metallic or carbide product. With the phosphorus removed, thereaction product heavy metal (carbide) concentrate is suitable forfurther extractive processing in a halogenation, fractional distillationthen dissociation route. The monazite used in this example containedLa;Ce;Th; in approximate atomic ratio of 3:1:1. Other phosphate mineralshave also been processed in a similar manner with comparable outcomes.The apparatus utilised to carry out the process of this example isdepicted in FIG. 2.

[0078] Firstly, the monazite concentrate, which had been derived formmineral sands, was prepared in a particulate form by milling to a grainsize of less than 10 micrometres, and intimately blended with a 10percent stoichiometric excess of a reductant in the form of fine purecarbon. The fine blend increases the available reaction interface area.

[0079] 100 grams of the blended monazite and carbon was charged into alow density alumina crucible 1 (see FIG. 2). The crucible 1, beingformed of low density alumina is microwave transparent. Themonazite/carbon blend was charged loosely into the crucible 1 withoutpacking to maximise its permeability.

[0080] A microwave transparent aluminium silicate based fibre-matinsulation wrap 2 covered the exterior of the crucible, insulating thesame so as to maintain heat within the crucible 1. A partially openinsulation lid 2 a was placed over the opening of the crucible toinsulate the same whilst allowing for the escape of gases andobservation of the crucible contents. The insulation wrapped crucible 1was then placed in a reaction chamber 3, in the form of a purpose-builtevacuable reaction chamber capable of operation from an effectively“full” vacuum of less than 0.1 kPa to 1000 kPa (approximately tenatmospheres). The crucible 1 was placed on a microwave transparentrefractory brick spacer 4 so as to position the monazite/carbon blendload toward the centre of the reaction chamber 3 so as to optimise itslocation within the applied microwave field and thereby optimise itsload potential.

[0081] The reaction chamber 3 was then sealed with a lid 5. An o-ring 6with the addition of vacuum grease was used to seal the joint betweenthe reaction chamber upper flange 7 and the lid 5. The flange 7 and lid5 were then externally clamped utilising a suitable clamp 8: A viewingport 20 was provided in the lid to enable visual monitoring of theprocess.

[0082] The sealed reaction chamber 3 was then evacuated via reactionchamber outlet 9 utilising a suitable vacuum pump. The reaction chamber3 was evacuated to the system dependant pump limit of less than 1 kPa,as monitored on a vacuum gauge 10. The reaction chamber 3 was thencharged for two minutes with high purity argon gas via gas inlet 11. Theevacuation/charge cycle was then repeated three times to ensuresubstantially all air within the reaction chamber had been replaced withthe argon gas.

[0083] Removing the air ensured all oxygen had been removed from thereaction chamber, leaving an inert atmosphere protecting reductionproduct from re-oxidation.

[0084] The argon supply was then turned off, and the reaction chamber 3evacuated to a minimum pressure of 40 kPa for the reduction operation,again with the system pressure being monitored via the vacuum gauge 10for stability over a 5 minute period.

[0085] The reaction chamber was then irradiated with microwaveradiation, with a power of 1 kW and a frequency of 2450 MHz, via atop-mounted wave guide 12. The wave guide 12 was arranged with amicrowave transparent ceramic window 13, formed of alumina, at theinterface with the reaction chamber 3 to seal the same and to insulateagainst radiant heat.

[0086] The remnant argon gas (at 40 kPa) in the largely evacuatedreaction chamber 3 was the ideal environment for the stimulation of anon-equilibrium plasma capable of initiating the initial solid statereduction of the monazite utilising the carbon as reductant, producingcarbon monoxide (CO) as a by-product of this initial solid statereduction. This initial solid state reduction can be represented byEquation 1(a) below:

(Ce,La,Th)PO₄+4C

(Ce,La,Th)OC+P+3CO

  1(a)

[0087] The CO produced in the above solid state reduction itself becomesan effective reductant, transferring carbon in a gaseous form to thereaction interface with greater efficiency. Significantly also for thekinetics of the reaction, the gaseous CO ionises in the microwavestimulated environment to augment the plasma and provide highly activepositive ion species (principally CO⁺) which are not present in theoriginal argon plasma. Whilst the argon plasma exhibits highly energeticnegative (including electrons), positive, re-combined and excitedspecies, it provides no reactive radical species. The ionisation of theCO and the gaseous phase reduction of the monazite can be represented byequations 1(b) and 1(c) below:

CO

CO⁺ +e  1(b)

(Ce,La,Th)PO₄+3CO

(Ce,La,Th)OC+P+3CO₂

  1(c)

[0088] The CO in Equation 1(c) may be in the ionised form CO⁺.

[0089] A further final reduction step from the oxycarbide to a (complex)metal carbide was exhibited, again using the CO (at least partlyionised) as reductant. The following Equation 1(d) can be used toreasonably explain this final step of the reduction process:

x(CeLa,Th)OC+yCO

(Ce,LaTh)_(x)C_(Y) +nCO₂

+mCO

  1(d)

[0090] Again the CO in Equation 1 (d) may be in the ionised form CO⁺.

[0091] Whilst this reduction to the carbide was confirmed throughanalysis, the very hot carbide showed a propensity to strip oxygen fromthe otherwise very stable oxide crucible (and other refractory materialin contact) and return much of the carbide product material to the morestable oxycarbide phase(s).

[0092] During the above reduction reactions, gases produced were drawnaway and pumped from the chamber via the outlet 9 during ongoingevacuation of the reaction chamber 3 such that the reaction chamberpressure always remained below 50 kPa (absolute). With this low pressurehaving been maintained throughout the process, the plasma sustained canbe well assumed to have remained well within non-equilibrium conditions.

[0093] The microwave radiation sustaining the plasma and the reductionreactions was continued until the distinctive CO plasma colour could nolonger be visually detected at the same intensity. This change in plasmacolour and intensity suggests that CO was no longer being produced,indicating that reduction had finished, along with an associatedreduction in pressure back down to the pump limit. At this stage theplasma is expected to have been a principally CO plasma, with the argonhaving largely been flushed through the system during the constantevacuation through the reaction chamber outlet 9.

[0094] One minute beyond this visually assessed point of reduced COplasma colour and intensity discussed above, and about 10 minutes afterplasma inception, the microwave power was shut off. Argon was bled intothe still evacuating chamber via the gas inlet 11, and the pressurestabilised at 20 kPa (absolute) for one hour (to include principalcooling through solidification). The vacuum pump was then disengaged andthe reaction chamber 3 sealed from the pump and backfled with highpurity argon to a modest positive pressure and kept thus until fullycooled before opening on the following day.

[0095] The reactor chamber 3 was slowly brought to atmospheric pressure,carefully opened so that no reaction product was disturbed, dislodgednor contaminated, and the crucible 1 removed from the chamber 3. Thecrucible 1 contained the reduced heavy metals carbide (oxycarbide)product, with ash and gangue slag atop. The heavy metals content of thecrucible 1 was scraped from the crucible wall and kept for analysis andfurther processing as desired.

[0096] The metal reaction chamber wall 1 and metallic solidificationbaffles 14, which protect the reaction chamber outlet 9 (forming thevacuum pump inlet) by collecting condensate of the hot vapour phasesbefore they escape through the outlet 9, were copiously coated in“fluffy” labile phosphorous. The recovered phosphorus was analysed aspure, elemental phosphorous as anticipated by Equations 1(a) to 1(d).The reactor components were then cleaned of reaction products inpreparation for further batch processing.

EXAMPLE 2

[0097] This example details a process to economically recover metals ofvalue from metallurgical wastes and slags using an in-crucible batchreduction process. Zinc was recovered from a zinc-bearing slag byreducing the metal in situ in the slag and recovering the metal asmetallic fume from the hot reacting bed. The zinc fume may, at thispoint, be re-oxidised to a refined grade of zinc oxide powder, orreacted with a halogen to yield a zinc halide. In the context of thisspecification, a fume is to be understood as including a metallic vapouror a metallic oxide, metallic halide or other similar vapour derivedfrom the metallic vapour.

[0098] The process was performed successfully at atmospheric pressure,in a gas mix of nitrogen and carbon monoxide, as opposed to the reducedpressure of Example 1. As metals such as zinc are less of an “oxygengetter” than the “reactive metals” (such as the La, Ce and Th of thereduced solid product phase of Example 1), the reduced zinc product ofthe present Example had a lesser tendency to re-oxidise, and hencerequired less protection against re-oxidation. Consequently, the processcould be carried out successfully at atmospheric pressure as thepropensity of the reduced product to re-oxidise was overwhelmed by thereducing conditions in the reaction environment of the reaction chamber.The desired fume product (metal, oxide or halide) dictated thecomposition of, and the related chemical possibilities for, the reactionchamber environment in which the zinc was reduced and fumed. In thepresent example, process efficiency and product quality were able to bemaintained by generating and sustaining a non-equilibrium plasma atatmospheric pressure, and hence the difficulty and expense of obtainingand controlling a reduced pressure reaction chamber environment wereavoided.

[0099] The apparatus utilised to carry out the process of this exampleis depicted in FIG. 3.

[0100] Zinc-bearing metallurgical slag material having a mineralogicalcontent of zinc oxide (ZnO), or a more complex mineralogy withZnO-equivalent, was ground into particulate form to a grain size of lessthan 500 micrometres and blended, to twice the stoichiometricrequirement (with respect to the ZnO), with a reductant in the form offine reactive charcoal. 100 grams of the blend was charged into analumina crucible 101. The charge was loosely packed to maximise thepermeability thereof. The base of the crucible 101 was configured withfine passages 101 a passing therethrough rendering the base porous toallow an updraught of gases through the loosely packed charge of slagand charcoal. The crucible was mounted on a rigid ceramic box 114 havingan open top communicating with the passages 101 a of the crucible base.The crucible 101 and box 114 were insulated with a microwave transparentaluminosilicate based fibre-mat wrap 102 to insulate the crucible 101from heat loss. The insulated crucible 101 and box 104 were then placedinto a reaction chamber 103, in the form of a purpose modifiedcommercially available 1300W microwave oven. The crucible 1 boxarrangement was placed on a suitable refractory brick spacer 104 tolocate the charge toward the centre of the reaction chamber 103, andhence favourably placed within the applied microwave field. The openingof the crucible 101 was partly covered by a loose, microwave transparentinsulation lid 102 a to allow the escape of fume reaction product whilstmaintaining much of the heat within the crucible 101. A viewing port 120in the roof of the reaction chamber 103 allowed for visual monitoring ofthe reaction process.

[0101] The reaction chamber 103 was closed and then simultaneouslyevacuated via an outlet 109 by a roughing pump whilst nitrogen gas wasbled into the chamber 103 via a primary gas inlet 111. After fiveminutes, the roughing pump was closed-off and the nitrogen supply wasincreased to a positive pressure to flush-out and fill the chamber 103.

[0102] The chamber 103 was not inherently airtight, and hence thepressure within the reaction chamber 103 remained at close toatmospheric pressure. After five minutes of flushing, the primary gasinlet 111 was closed. A reductant gas mixture of 20% CO in nitrogen wassupplied at a low flow rate to the box 114 via a secondary gas inlet 115communicating therewith through the bottom of the reaction chamber 103.The supply of reductant gas to the box 114, at a positive pressure,resulted in the reductant gas passing through the passages 101 a in thebase of the crucible 101 and permeating through the slag/charcoalcharge.

[0103] The reaction chamber 103 was then irradiated with microwaveradiation of frequency 2450 MHz and applied power of 1300W, via twocounterposed waveguides 112 sealed from the reaction chamber 103 bymicrowave transparent ceramic windows 113. After several minutes ofirradiation, heating the slag/charcoal charge and gases within thereaction chamber, random thermal runaway in disparate, dielectricallydisposed particles initiated the generation of a CO/N₂ plasma in andabove the crucible 101 within the reaction chamber 103. This plasmacould be observed through the shielded viewing port 120.

[0104] By operator interpretation of plasma extent and radiant heatintensity, microwave inadiation of the reaction chamber 103 wascontinued with the applied power being manually adjusted to provideapparent thermal constancy and to avoid overheating and failure of thecrucible 101 by melting. From prior experience and the examination of,and knowledge of the melting points of phases present and from reactionthermochemistry data, it was estimated that the process was operated at“temperatures” equivalent to the range 900° C. to 950° C. As previouslydiscussed, the concept of temperature in a dynamic thermal system suchas a non-equilibrium plasma is relatively meaningless, and accordingly“temperature” measurement by thermocouple or direct line-of-sightpyrometry methods is impracticable and would provide almost meaninglessinformation.

[0105] Approximately one to two minutes after plasma initiation, ametallic fume was readily detected rising from the plasma, indicatingreduction of the zinc oxide content of is the slag. The solid andgaseous state reduction of the zinc oxide, utilising the charcoal and COplasma as reductants respectively, can be represented by Equations 2(a)and 2(b) below:

ZnO+C

Zn+CO

  2(a)

ZnO+CO

Zn+Co₂

  2(b)

[0106] The CO in Equation 2(b) may be in the ionised form CO⁺.

[0107] The metallic fume is particularly easy to visually detect if ithas been allowed to reoxidise as it leaves the reducing atmosphere ofthe crucible 101, after having been separated from the slag by thereduction processes of Equations 2(a) and 2(b).

[0108] To produce a finely divided zinc oxide (ZnO) powder oxide, anoxygen (O₂) stream was introduced such that the reduced zinc metalvapour passed through the O₂ stream, rapidly converting it to a solidzinc oxide phase fume which could be easily collected. Whilst simplypassing the zinc metal vapour through CO₂ already within the reactionchamber environment as a reduction by-product of Equation 3(b) also hadthe effect of oxidising the zinc vapour, this reaction is lessspontaneous and resulted in some of the zinc fume remaining unconvertedas solid zinc fume. To produce zinc chloride (ZnCl₂), Cl₂ gas can beintroduced across the hot zinc vapour. The zinc chloride produced had tobe cooled significantly before a solid fume product could be collectedby precipitation onto a cool surface. The re-oxidation processes can berepresented by Equations 2(c) to 2(e) below:

Zn+O₂

2ZnO

  2(c)

Zn+CO₂

ZnO+Co₂

  2(d)

Zn+Cl₂

ZnCl₂

  2(e)

[0109] The fume product, in the form of metallic zinc, zinc oxide or azinc halide dependant on system atmosphere, was extracted away through amicrowave transparent borosilicate fume hood 116 placed over thecrucible 101 by an extractor fan to a precipitation and bagging system,via a vacuum seal tap, where the fume was collected as solid fines.

[0110] Once the fuming had died away to a visually imperceptiblequantity, the process was deemed to have finished and irradiationceased. Completion of the process was later confirmed by analysis of theslag material remaining in the crucible.

[0111] Immediately after the irradiation had ceased, the contents of thecrucible remain reactive and at a high temperature for a prolongedperiod, bleeding of the reducing CO/N₂ gas mixture through the cruciblewas continued until the charge cooled to about 200° C. Continuedbleeding with nitrogen was then used to cool the system to ambienttemperature.

EXAMPLE 3

[0112] This example details a process to reduce chromite (FeO.Cr₂O₃) oreconcentrate using an in-crucible batch reduction process resulting in achromium iron alloy. The apparatus utilised to carry out the process ofthis example is depicted in FIG. 4.

[0113] The process was carried out at atmospheric pressure, which provedadequate for this example. Further, rather than charging the reactionchamber with a gas mixture of nitrogen and carbon monoxide as perExample 2, air (composed principally of N₂, O₂) was utilised as theinitial gas in the reaction chamber. Combustion of char through heatingand micro-arcing of the char in the oxygen rich environment to produceCO was sufficient to protect against re-oxidation of reaction product.Further, molten slag covers the reduced metallic product phases toconfer further protection in this example, enabling the simpler and moreeconomical processing option of an atmospheric pressure air environment.

[0114] High grade chromite ore concentrate was ring-milled with areductant in the form of brown coal char in stoichiometric quantity to agrain size of less than 200 micrometres. The blend was loosely chargedinto a suitable microwave transparent oxide ceramic crucible 201, atop abed of granular char to allow for pooling of liquid metal productsbeneath the reactants. A further layer of granular char was laid overthe chromite/coal char blend charge to assist with protection fromre-oxidation. As per Examples 1 and 2, the crucible 201 was insulatedwith an aluminosilicate fibre insulation wrap 202 and a lid 202 aconfigured to allow limited observations through the viewing port 220and allow gaseous reduction products to escape.

[0115] The insulated crucible 201 was placed into the reaction chamber203, in the form of a modified commercial microwave oven on a ceramicbrick 204, “charged” with air at atmospheric pressure. No flushing orevacuation was carried out.

[0116] The reaction chamber 203 was then irradiated with 2450 MHzmicrowave radiation at full 1300W oven power via top and side mountedwaveguides 212. The reactant charge in the crucible 201 heated rapidlydue to micro-arcing between char particles and then betweendielectrically different particles in the charge blend, leading to theonset of some chemical reactions of lower activation energyrequirements. The release of energy from these initial exothermicreactions provided further thermal energy to further heat and activatereduction reactions.

[0117] The initial micro-arcing, in the applied microwave field, of thechar in the oxygen containing air environment generated CO, according toEquation 3(a) below, providing protection against re-oxidation ofsubsequent reduction reaction product:

2C+O₂

2CO

  3(a)

[0118] As the reactant charge increased in temperature, with massivedeviations in local temperatures across a random temperature profile, anon-equilibrium nitrogen plasma was generated in the principallynitrogen (air) atmosphere of the reaction chamber 203, with heatingsubsequently becoming more even throughout the reactant charge. With thehighest temperatures being established in and above the reactant chargewithin the crucible, the plasma was concentrated within the upper levelsof the reactant charge (through plasma penetration of the staticcharge), and directly above the reactant charge within the crucible, 201below the insulating lid 202 a. The radiation, and the plasma, penetratedeeper into the static in-crucible charge with increased permeability ofthe charge.

[0119] The nitrogen plasma stimulated initiation of the solid statereduction of the chromite utilising the charcoal as initial directreductant, producing carbon monoxide (CO) as a by-product of this solidstate reduction and which ionises, contributing to the plasma chemistry.The reactions produce chromium metallic product, leaving a wustite (FeO)rich phase to be reduced in a second stage. This result may be explainedby the greater microwave susceptibility of Cr₂O₃ than FeO (to heat in amicrowave field). The initial solid state reduction of the chromite canbe represented by Equation 3(b) below:

FeO.Cr₂O₃

3C>2Cr+FeO+3CO

  3(b)

[0120] The CO produced from Equations 3(a) and 3(b) is notthermodynamically stable below approximately 950° C. when in anenvironment containing oxygen, such as that of the present example, and,on cooling, tends to oxidise with the oxygen present in the airatmosphere to carbon dioxide (CO₂), according to Equation 3(c) below:

2CO+O₂=

2CO₂

  3(c)

[0121] With increasing temperature, however, at the “temperatures”experienced in the plasma, the inverse is generally true, with freeoxygen and carbon dioxide gas molecules existing in the atmosphere ofthe reaction chamber 203 directly above the reactant charge beingthermochemically predisposed towards conversion (with char) to carbonmonoxide, according to Equations 3(d) and 3(e) below:

O₂+2C

2CO

  3(d)

CO₂+C

2CO

  3(e)

[0122] The CO produced by these reactions itself ionises in themicrowave stimulated environment to augment the predominantly nitrogenplasma with highly energetic, reducing CO⁺ ions. In the reaction chamberenvironment, the plasma enveloping the reactant charge at the higherreducing “temperatures” is accordingly composed primarily of N₂ and COspecies. The plasma protects the charge from possible oxidationreactions to the plasma extremities, maintaining a blanket of highenergy reducing ions over the charge providing a highly reductiveenvironment. Such protection is provided for by the nature of plasmas,and particularly non-equilibrium plasmas, the “chemical emphasis” ofwhich are to break bonds in a manner analogous to chemical reductionreactions (that is, opposite to chemical oxidation reactions where bondsare completed).

[0123] The shift in plasma cheinstry with the generation of CO⁺ ionscould be visibly observed as a shift in the characteristic emissioncolour of the plasma and audibly detected by an associated shift inpower drawn at the magnetrons where there is plasma initiation orstep-augmentation.

[0124] The CO available in the ground, excited, ionised and recombinedstates becomes an effective reductant, transferring carbon to thereaction interface with the chromite particles, initiating a gaseousphase reduction of the chromite. At this stage the reduction ratesincrease to a maximum. The ionisation of the CO and the ionised gaseousphase reduction of the chromite can be represented by equations 3(f) and3(g) below:

CO

CO⁺ +e ⁻  3(f)

FeO.Cr₂O₃+3CO⁺+3e ⁻

2Cr+FeO+3CO₂

  3(g)

[0125] As discussed above, the CO₂ produced will tend to CO (accordingto Equation 3(e)) at the high plasma “temperatures” experienced at thisstage. The subsequent solid and gaseous state reduction of the wustite(FeO) product of Equations 3(b) and 3(g) to metallic iron can berepresented by Equations 3(h) and 3(i) below:

FeO+CO⁺ +e ⁻

Fe+CO₂

  3(i)

[0126] Where desired, other initial reductant gas (typically CO) can beintroduced preemptively to the reaction chamber 203 via the primary gasinlet 211 to assist the various reduction processes. This will provide areductive gas environment in the reaction chamber from the onset ratherthan relying on conversion of the O₂ within the air environment to CO asdiscussed above.

[0127] Hot gases, including reaction by-products CO and CO₂, plus minorand trace gases, dust and fume were extracted during the process via afume hood 216 communicating with an exhaust gas-handling system.

[0128] During the reduction process, metallic reduction product reportedin the liquid state as liquid metal beads, and as the individual beadsgrew in size and surface tension was overcome, the liquid metallic phaseflowed to the base of the crucible 201 forming a pool 230 beneath a slagphase 231 of gangue products, which itself formed below the stillreacting bed of reactant charge 232 until the depleting solids of thereactant charge bed 232 melted into the liquid slag phase 231. At thispoint, the microwave irradiation was ceased and the process terminated.

[0129] The reaction chamber 203 was then allowed to cool with the metalreaction product and slag phases solidifying enabling mechanicalrecovery. Passive, slow cooling beneath glowing char (to conferprotection from oxidation) produced a “grey” alloy iron, whilst thealternative cooling process of cooling in water produced a “white” ironalloy.

[0130] To avoid oxidisation of the metallic product during cooling asthe temperature within the crucible drops below the CO stability pointof approximately 950° C. at which the CO would oxidise to the oxidisinggas CO₂, a non-oxidising or inert gas can be introduced to the reactionchamber through the primary gas inlet 209 during cooling. Spectroscopicanalyses and metallographic examination of the metallic reaction productidentified a chromium iron alloy with a typical composition ofapproximately 65 at % Cr (and up to 76 at % Cr in minor iron beads),less-than 4 at % C, and the balance principally Fe. The C intakeincreases with extended time at elevated temperature. All mineral matterwas converted either to metal or slag, with only remnant char remainingabove the slag phase.

EXAMPLE 4

[0131] This example details a process to reduce cassiterite (SnO₂)concentrate to extract metallic tin as product. Rather than beingcarried out in a fixed crucible within a static vessel or a modifiedmicrowave oven as per Examples 1 to 3, in this example the reductionprocess was carried out in a fluidised bed reactor, utilising a carbonmonoxide/nitrogen plasma. The fluidised bed reactor configuration isdepicted in FIGS. 5(a) to 5(d). The plasma reduction process can also becarried out in other established and hybrid reaction chamberconfigurations, including rotary kiln, cyclone, conveyor strand, screwand launder configurations, using the same basic process chemistry.

[0132] The process was conducted at blast-ambit “atmospheric” pressurehigh in the bed to higher pressures at the fluidising plate (between 200kPa and 300 kPa) where initial reduction processing may be conducted viaapplied microwave energy supplied through the reactor base waveguide.Pressure drop through the fluidised bed is dictated by fluidisationdynamics of the reaction chamber and various parameters of the bed beingfluidised itself, including the bed height, particle density, shape andsize range. A non-equilibrium plasma was sustained along the full heightof the reaction chamber column with the assistance of supplementarywaveguides along the length of the reaction chamber, the application ofwhich will be dependent upon mineral density, charge susceptibility tomicrowave radiation and applied power. With the pressure drop throughthe fluidised bed, the non-equiliblium plasma was more stable towardsthe top of the reaction chamber.

[0133] The current example carried out the reduction processing of a“low grade” cassiterite concentrate, containing approximately 60% Sn.Using, traditional reduction techniques for Sn, using reverberatoryfurnace smelters, grades below 65% Sn are undesired as it is noteconomically feasible to process tin product, with the ratio of“hardhead” (iron/tin phase) to recovered tin being too high. When ironis readily reduced with the tin producing the iron/tin hardhead phase,or the ratio of iron in the initial concentrate is high, the traditionalreduction techniques are typically commercially untenable due to theexcessive cost of extracting tin from the iron/tin hardhead phase. Theease of reduction of cassiterite concentrates increases with increasingtin content from low grade to high grade concentrates, with higher gradeconcentrates having been found to be more susceptible to microwaveradiation than lower grade concentrates.

[0134] Fluidised bed reactors are commonly configured to carry outcontinuous processing operations, however the present process wascarried out in a fluidised bed reactor configured for and operated as abatch process to enable tighter control over the cassiterite processingtimes within the reaction chamber. Such tighter control when processingcassiterite is desired to avoid over-processing of the cassiteritecharge which would be detrimental to post processing operations. Thecontinuous fluidised bed process is preferred, however, when lesscontrol is required on the reduction exposure to the appliedelectromagnetic radiation.

[0135] When the plasma process of the present example is utilised witheither batch or continuous fluidised bed systems, the simultaneousreduction of gangue materials within the ore, particularly ferruginousminerals, is avoided. This consequently avoids the formation ofcontaminant phases (particularly hardhead, FeSn₂) within the reductionproduct and the associated restrictive cost penalties of re-processingsuch by-products in subsequent operations.

[0136] The fluidised bed reactor 300 of FIGS. 5(a) to 5(d) utilised inthe present process comprises an elongated reaction chamber 301 formedof high temperature strength, corrosion resistant alloy steel. Thereaction chamber 301 is insulated with a suitable refractory insulationwrap 302 to maintain heat within the reaction chamber. An air gap may beformed between the outer wall of the reaction chamber 301 and theinsulation wrap 302 to isolate vibration and accommodate expansion.

[0137] A reactant charge inlet 303 is provided at the top of thereaction chamber 301 for charging the reaction chamber 301 with theparticulate reaction charge. Referring to FIG. 5(b), a retractable, selfsealing charging bell 304 is disposed within the reactant charge inlet303. The charging bell 304 is rotatable and is provided with spirallingvanes 305 to assist in charge distribution within the reaction chamber301. Other forms of device for charging the reaction chamber, such as arotating chute, may alternatively be employed.

[0138] A perforated fluidising plate 306 is located at the base of thereaction chamber 301. A fluidising wind box 307 is located below, andopens onto, the fluidising plate 306. The fluidising wind box 307communicates with a gas regeneration system (described below anddepicted in FIG. 5(c)) upstream supplying gas to the wind box 307. Thecomposition and pressure of blast gas supplied to the wind box 307 iscontrolled by a monitoring system 308.

[0139] An exhaust outlet 309 is located adjacent the charge inlet 303 atthe top of the reaction chamber 301. The exhaust outlet 309 feeds afume/solids product extraction system (not depicted) to separate fumeand solids fines product from exhausted gases. This system then recyclescooled de-fumed gases into the chamber 310 of the gas regenerationsystem (see FIG. 5(c) via a recycle outlet 311. The chamber 310 isfurther provided with a fresh gas inlet 312 for introduction of gasesfrom outside of the regeneration system, and a pressure relief valve andoutlet 313 for the escape of gases under excess pressure.

[0140] A discharge chute 314 communicates with the reaction chamber 301directly above the fluidising plate 306 for the discharging of batchprocess charges upon completion of processing of each batch. The chute314 is closed during processing and communicates with a quenchingchamber 315 for cooling/quenching of discharged material.

[0141] Top and bottom waveguides 316, 318 are located at the top of thereaction chamber 301 adjacent the reactant charge inlet 303 and at thebottom of the reaction chamber adjacent the fluidising plate 306respectively. The top waveguide 316 is positioned to irradiate the topregion of the reaction chamber, where off-take gases produced byreactions in the reaction chamber will be present. The bottom waveguide318 is positioned to irradiate the bottom region of the reaction chamberabove the fluidising plate 306. It is at this region that the reactionchamber pressure will be greatest. Further supplementary waveguides 317were located around the periphery of the reaction chamber 301, spacedbetween the top and bottom, and about the circumference thereof (seeFIG. 5(d)). The number, radiating frequency and arrangement ofwaveguides is dependent on the specific application, and in particularwill depend on the reaction chamber configuration and thecharacteristics of the charge being processed. Microwave irradiation at2450 MHz, total power variable up to 100W per port, was utilised in thepresent example. The general location and orientation of thesupplementary waveguides 317 depicted in FIG. 5(d) is preferred formultiple waveguides positioned along the reaction chamber 301. Ratherthan delivering the radiation utilising waveguides, coaxial cables orany other suitable delivery means could be employed.

[0142] In the process of the present example, the cassiteriteconcentrate was first prepared in particulate form with a grain size ofless than 500 micrometres and in batches of close size ranges (+/−5% ingrain diameter), which are preheated to 200° C. in preparation forcharging into the reaction chamber 301.

[0143] Preheated air was then passed, via the wind box 307, through thefluidising plate 306 into the closed reaction chamber 301 and outthrough the exhaust gas outlet 309. Once the reaction chamber proper hadreached approximately 250° C., the preheated air blast was replaced byan N₂/CO mixture (at an N₂:CO ratio of approximately 4:1) preheated toapproximately 300° C. charged into the system from the fresh gas inlet312 of the gas regeneration system. The CO gas was added to form theionising reductant for the reduction of the cassiterite.

[0144] Whilst flushing the reaction chamber 301 with the N₂/CO mixture,the pre-heated cassiterite concentrate was charged into the reactionchamber 301 through the reactant charge inlet 303 until a full chargewas achieved, and taking care during charging to adjust blast pressureof the N₂/CO mixture such that the incoming charge material did notsieve through the fluidising plate and that the fine charge material wasnot blasted out of the chamber with the exhaust gases. During charging,the charging bell 304 was manipulated to regulate and distribute thereactant charge, and in combination with regulation of the N₂/CO blastpressure passing upwards into the reaction chamber 301 through thefluidisation plate, fluidisation of the charge was established andmaintained, whereby the fine charge was maintained in a turbulentsuspension or “fluidised bed” 320. This fluidised bed of reactantparticles maximises the reaction interface between the cassiteritecharge and the gaseous CO reductant.

[0145] The fluidisation regime was established such that the fluid bedwas sufficiently stable and dielectrically incoherent to allowpenetration of microwave irradiation from the various waveguides 316,317, 318.

[0146] To establish and maintain such a fluidisation regime which isstable and allows penetration of the radiation, the fluidising gasstream through the fluidising plate 306 should be incident at the bedbase at such a pressure as to force the gas, lifting and fluidising thereactant charge bed, towards the zone of lower pressure at the bedstockline (top surface of the bed toward the top of the reactionchamber), where operating pressure should be as low as or close toatmospheric pressure as possible (in the absence of a vacuum evacuationsystem) so as to minimise the required fluidising pressure. The pressuredrop between the fluidising plate 306 and the stockline (which should beminimised) is determined by the fluidisation dynamics of the bed inparticular the particle size, density, size range, bed permeability andviscosities, and by the height of the bed. The fluidising pressure atthe fluidising plate 306 is determined by providing the desiredfluidising regime whilst minimising the top pressure at and above thebed stockline. This pressure at the fluidising plate 306 is controlledby the pressure sustained in the wind box 307. The wind box pressuremust equate to the fluidising pressure plus the pressure drop across thefluidising plate 306, and was monitored and controlled by the gasre-generation system 310 and the feedback control system 308.

[0147] The process pressure range, of which the fluidisation pressure atthe fluidisation plate will be the maximum, should be kept below 300 kPato maintain the plasma within the non-equilibrium thermodynamic regimeto maximise the processing benefits of highly energetic reactiveparticles, particularly those particles taking a direct role in theplasma reduction chemistry.

[0148] The reaction chamber was then irradiated with microwave radiationat 2450 MHz frequency via the waveguides, and the power adjusted until astable nitrogen/carbon monoxide non-equilibrium plasma was formed tofull charge height with predominant CO⁺ reactive ions. The common 2450MHz microwave frequency used for this and other examples described wasfound to be highly suited to the applications, and was used primarilyout of convenience. Other frequencies within the range of 30 MHz to 300GHz, radio frequency though microwave and into the “millimetrewavelength” frequencies have, however, been found to be variously wellsuited to the generation of non-equilibrium plasmas preferring anexploitable range of target mineral susceptibilities.

[0149] The fluidised cassiterite was reduced by the gaseous CO in thevarious states (ground, excited and ionised), to form Sn and CO₂. Theplasma phase reduction can be represented by equation 4(a) below(where * represents a non-ground state re-combined particle or species):

SnO₂+2CO⁺+2e

Sn+2CO₂*   4(a)

[0150] Once the plasma chemistry was stabilised, fine carbon wasinjected through the fresh gas inlet 312 to mix with the fluidisingblast gas (N₂/CO), such that CO was regenerated from the CO₂ generatedduring the gaseous phase reduction of cassiterite, thereby ensuring acontinuing supply of CO⁺ ions for the ongoing reduction of thecassiterite. This reaction, known as the Boudouard reaction, isrepresented by equation 4(b) below:

C+CO₂*

2CO  4(b)

[0151] The Boudouard reaction is endothermic, and hence should only beemployed when “temperature” moderation is appropriate. This reactionwill also only proceed effectively at temperatures above about 940° C.Where, as a result of the above, the Boudouard reaction is not tenable,CH₄ can be utilised both as a reductant (both directly as methane orindirectly at temperatures above that at which methane decomposes tocarbon plus hydrogen) to reduce the cassiterite ore and to regenerate COfor further reduction. Alternatively, CH₄ can be utilised both forregeneration of CO by reduction of CO₂ during the process and as apartial or total replacement for CO in the initial input gas mixture asinitial reductant for the reduction of the cassiterite. Whilst the CH₄itself does not ionise, dissociating (decomposing) at temperatures below500° C. in the microwave field before it reaches its ionisation energy,the resultant hydrogen gas does form a plasma, as will the initialreduction product CO as soon as it is produced, acting as a reductantfor subsequent plasma phase reduction. Further, fine carbon soot isproduced as a by-product of the methane decomposition, which is idealfor re-generation of CO. Accordingly, even when CO is not used as aninitial input gas, it is soon formed as a reduction by-product and/orthrough the Boudouard reaction breaking down CO₂ at high temperatures.The addition of methane to the fluidising gas can also be used toreplace the addition of solid carbon fines to the fluidising gasdiscussed above to enable the CO-regenerating Boudouard reaction 4(b).

[0152] At the lower energy or “temperature” ranges of non-equilibriumplasmas, hydrogen is a less efficient reductant than carbon or carbonmonoxide. Further, the Boudouard reaction, being endothermic, takesenergy from the system in supplying CO. Accordingly, selecting CH₄ asinitial gas input is a lower thermodynamic energy option in whose lowerenergy conditions “tramp elements”, such as Fe, Mn, W and Si which maybe contained in the ore reactant charge, will have lower probability ofbeing reduced with the easier to reduce cassiterite, providing a morepure reduction product.

[0153] Furthermore utilising CH₄ introduces another gas to the systemwhich results in a more complex off-take gas mixture requiring treatmentand separation. The chemical reactions associated with the introductionof CH₄ can be represented by equations 4(c) to 4(g) below, plus theBoudouard equation 4(b).

CH₄

C+2H₂   4(c)

SnO₂+2C

Sn+2CO  4(d)

SnO₂+2CO

Sn+2CO₂  4(e)

2H₂

4H⁺+4e ⁻  4(f)

SnO₂+4H⁺+4e ⁻

Sn+2H₂O  4(g)

[0154] Additional chemical reactions of significance with respect to thegas mixture components in the reaction chamber atmosphere (with theaddition of methane) can be represented by Equations 4(h) and 4(i)below:

2CO+CH₄

2C+2H₂O  4(h)

N₂+CO₂+2CH₄

2C+2NH₃+CO+H₂O  4(i)

[0155] These reactions are also of significance to the control ofoff-take gases, minimising negative environmental impact and therecovery of process by-products as materials of value. These reactionstake place in the reaction chamber and, where desired, may be extendedto completion in an augmentative chamber of the exhaust outlet 309.Because stoichiometry is preserved, Equations 4(h) and 4(i) have beengeneralised here in the ground state form for simplicity. Carbonmonoxide and nitrogen will be ionised, whilst (if not alreadydissociated) methane will dissociate to soot plus hydrogen which willionise. Also, other reactions and outcomes are possible but less stable,and thus unlikely.

[0156] During processing, off-take gases were exhausted through theexhaust outlet 309. The exhaust can then be drawn off to a cyclone toseparate and remove entrained solid fumes from hot off-take gases boundfor scrubbing or recycling (re-generation).

[0157] Reduction of the cassiterite produces tin (as indicated inequation 4(a)) in the form of micro liquid beads which form within thecassiterite particles and on the particle surfaces, where they are heldtightly by the inherently high surface tension of liquid tin plus a filmof higher melting point material being re-fused or reduction by-productsof gangue minerals.

[0158] At a processing point determined by experience and an analysedmean of the accumulated data (charge vs time vs applied energy) withrespect to degree of reduction of all prior process batches, microwaveirradiation of the reaction chamber 301 was ceased. The particulatematter of the still fluid bed was then cooled to about 200° C. in anon-oxidising blast gas (nitrogen was used in this example) to solidifythe tin. The solid contents of the bed were then discharged from thereaction chamber 301 through the discharge chute 314 into the quenchingchamber 315 for further oxygen-free quenching (where required).

[0159] The metallic tin content can then be recovered from the quenchedsolids content by a suitable electrochemical or other recovery process.After recovery of the high purity tin, remaining incompletely reducedcassiterite or other mineral particulate material can be dried andreturned for re-processing through the fluidised bed reactor in asubsequent charge blend. Any other fines remaining from the tin recoveryprocess can be subjected to further extraction processes to extract anyremaining high-value metallic content (or toxic content requiringseparation and disposal) which may include metals such as Au, Ag, Th,RE's, Ta, W or Bi.

EXAMPLE 5

[0160] In the extractive reduction of comparable metal sulphides of theform MS₂, the “first” sulphur atom can be stripped by reduction withrelative ease to yield the matte form, MS. Typically, in a secondreduction stage, more intense pyrometallurgical operations are requiredto remove the remaining sulphur to produce the primary metal.

[0161] This example details the reduction of molybdenite (MoS₂) oreconcentrate in the solid state to yield a crude sponge molybdenummetal—apparently “sintered” by lower melting point phases (gangue andimpurity metals). The reduction to metal was achieved in a continuoussingle stage operation which utilised the pneumatics of a plug flowfluidised reactor to moderate and balance the applied electromagneticenergy and equably stimulate reactions with an even distribution ofenergy through the descending column of charge material. The apparatusutilised to carry out the process is depicted in FIG. 6.

[0162] The plug flow fluidised bed reactor 400 utilised was configuredfor continuous processing. In such a reactor, blast gas is directed froma blast box 407 into the reaction chamber 401 though a perforatedfluidising annulus 406 which takes the place of the fluidising plate ofExample 3. In contrast to the batch configured reactor 300 of Example 3,reactant charge material is intermittently or continuously charged viathe charging bell 404 (or a rotating chute equivalent), is fluidised bythe ascending blast gas, the descending fluid bed obeying the mechanicsof plug flow. The plug flow solids are subject to the reactions of theprocess to completeness, before being passed out of the reaction chamber401 through the open discharge funnel 414 in the centre of thefluidising annulus 406 into a quenching chamber 415. Reactant chargematerial is continuously charged into the reaction chamber 401 andreaction product solids continuously discharged without closing down thereactor.

[0163] In the present example, the molybdenite ore concentrate wasprepared in particulate form with a grain size of less than 200micrometres, and blended with a solid reductant in the form of granularcharcoal of size range 100 to 1200 micrometres in the stoichiometricratio of 2:1 C:S. Selection of granular charcoal in this larger sizerange was imposed to provide better bed permeability given theplate-like morphology of molybdenite. The molybdenite/charcoal blendcharge was then preheated to approximately 300° C. in preparation forcharging into the reaction chamber 401.

[0164] At the beginning of the continuous process, preheated air wasflushed through the reaction chamber 401 via the wind box 407 andfluidising annulus 406 into the reaction chamber 401 proper and outthrough the exhaust gas outlet 409. Once the reaction chambertemperature had reached approximately 300° C., the preheated blast airwas replaced by a mixture of 10% CO in air which had been preheated toapproximately 300° C., and, upon process start, increased to 600° C. ata rate of 10C° per minute.

[0165] Whilst flushing the reaction chamber with the CO/air mixture atlow blast pressure such that solid fines were not entrained andexhausted with the off-take gases, the preheated molybdenite/carboncharge blend was charged into the reaction chamber 401 (at thecalculated rate of charging for the continuous operation) via thereactant charge inlet 403 and charging bell 404. An initial charge ofthe charge blend formed a temporary discharge funnel plug in thedischarge funnel 414 between the closed discharge control valve 419 andthe first charge of material above the fluidising annulus 406 subjectedto full processing once a continuous plug flow had been initiated. Oncecontinuous plug flow had been initiated, the discharge control valve 419was opened. The first exiting unprocessed and under-processed materialwas removed from the quench chamber system and returned for blendingwith fresh blend material. Whilst the reaction chamber column wasreaching full charge, and during the start-up stage, the newly fluidisedbed was monitored so as to establish and preserve the plug flow regimewhich optimises full metallurgical conversion (by analysis) versus meanresidence time (in the reaction chamber). The fluidised bed regime wasestablished with sufficient fluid bed stability and dielectricincoherence to allow penetration of microwave radiation from the variouswaveguides 416, 417, 418 placed at the top, sides and base of thereaction chamber 401 in a similar manner to Example 3.

[0166] Reaction chamber top pressure (pressure above the bed stockline)should be as close to one atmosphere as is possible (given the pressuredrop through the bed from the pressure at the base required to maintainthe fluidisation regime), enabling the fluidisation pressure at the baseof the reaction chamber to be maintained below the preferred 300 kPa islimit.

[0167] Although short wavelength electromagnetic frequencies in rangesabove 12 GHz would have been preferred, as a result of the enhancedsusceptibility of molybdenite at these frequencies indicated by resultsof mineral susceptibility vs irradiating frequency analyses, radiationat the common frequency of 2450 MHz was used out of availability andconvenience (and found to be adequate for the purpose). Once the chargein the reaction chamber 401 had stabilised near the blast temperature ofapproximately 600°, the reaction chamber was irradiated with microwaveradiation via the various waveguides 416, 417, 418. The power appliedwas adjusted until a stable plasma was formed with predominant CO⁺reactive ions in the nitrogen plasma. The CO⁺ ions were formed followingconversion of O₂ and CO₂ in the presence of charcoal, as the reactionchamber temperature increased beyond 950° C. as discussed in earlierExamples, with the reaction chamber “temperature” increasing to theideal plasma reduction “temperature” of 1050° C. to 1100° C. (asmeasured by shielded thermocouple).

[0168] Whilst the exact reduction route achieved is not simple, theaddition of small quantities of lime (CaO) to the reactant charge blend,or pelletised molybdenite/lime/brown coal paste dried pellets of closesize range, here 1.5 mm±0.1 mm to 3.0 mm±0.2 mm, which were ideal forbed permeability and reduction chemistry with increased kinetics, hadthe effect of assisting reduction kinetics and reaction completeness.

[0169] Prominent reduction reactions which are understood to haveoccurred during processing are represented (without ionisationequivalents) in Equations 5(a) to 5(d). Equations 5(a) represents theinitial stripping of the first sulphide atom from MoS₂ and thesubsequent reduction to elemental molybdenum being represented byEquation 5(b):

MoS₂+O₂

MoS+SO₂  5(a)

2MoS+C

Mo+CS₂  5(b)

CS₂+2O₂

C+2SO₂  5(c)

[0170] Equations 5(d) and 5(e) represent the alternative route when limeis added:

MoS₂+2CaO

MoO₂+2CaS  5(d)

MoO₂+2C

Mo+2CO  5(e)

[0171] Once plasma chemistry has stabilised, fine carbon may be injectedwith the fluidising gas mix such that, where required, CO is regeneratedfrom O₂ and CO₂ (generated during reduction) with the carbon high in thereaction chamber to confer the protection of a reducing atmosphere in asimilar manner to Example 4. As discussed in relation to Example 4, TheCO₂ reduction, the Boudouard reaction, is endothermic and the balance ofreactions in the reactor can be manipulated such that reactor“temperature” profiles can be maintained as was the case for the earlierexample.

[0172] Again in a similar manner to Example 4, CH₄ can be introducedboth to regenerate CO and to provide an extra control mechanism (inaddition to control of the applied electromagnetic radiation) bybalancing the chemical energy released by exothermic reactions and thatabsorbed by endothermic reactions within the reaction chamber. Thevarious reactions resulting from the addition of CH₄ are as per those ofEquations 4(c), 4(b), 4(f), 4(h) and 4(i) discussed in relation toExample 4. It should be noted that whilst hydrogen increases itsefficiency as a reductant in the higher operating temperatures of thepresent process, it does not eclipse carbon monoxide in reductionefficiency until much higher temperatures (above 2000° C.). Furthermore,the dissociation of methane to provide active hydrogen will result inthe production of hydrogen sulphide (H₂S) gas which is normally a lessdesirable offtake gas option. The additional reduction reactionsresulting from the generation of hydrogen ions through the addition ofmethane can be represented by Equations 5(f) and 5(g):

MoS₂+2H⁺

MoS+H₂S  5(f)

MoS+2H⁺

Mo+H₂S  5(g)

[0173] At the base of the reaction chamber 401, the loose, fluid productparticulate solid of the descending bed was discharged through thedischarge funnel 414. The rate of descent in the bed was controlled bythe rate of discharge of processed solid material through the dischargefunnel 414 which is governed by the setting of the discharge controlvalve 419. Reaction chamber residence time is dictated by rate of plugflow descent (of charge elements), which (given unhindered particulatefluidity) is controlled by the discharge rate, which is regulated by thedischarge control valve setting. Residence time is determined by thethermochemical processing parameters (such as chemical availability,contact and reaction interface diffusion, chemical species, availableenergy and energy required) and the physical and chemical kinetics whichdetermine the overall rate of chemical conversion, thence the timerequired for chemical conversion. The time required for chemicalconversion should ideally be slightly less or equal to the designatedresidence time of reactant material in the reaction chamber.

[0174] The discharged material entered the quenching chamber 415 whereit was kept mobile during cooling to minimise agglomeration of particlesand to prevent bulk “sintering”. The particulate solid product is in aform which can be easily managed and handled, and may be sent forfurther refining stage processing such as an arc or ion beam melt, zonerefining operation.

[0175] As product was continuously discharged from the fluidised bedreaction chamber (column) 401, fresh charge blend material wascontinually charged onto the stockline of the fluidised bed in an evenmanner such that the stockline level remained constant.

EXAMPLE 6

[0176] This example details a process to reduce haematite (Fe₂O₃) usinga conveyor to pass reactant charge material through an atmosphericpressure reaction chamber in a continuous process. The apparatus, termeda continuous conveyor fed reactor, utilised to carry out the process isdepicted in FIG. 7.

[0177] Fine haematite was blended with a reductant in the form of finebrown coal char, the mixture was bound into a paste using brown coalslurry to result in an Fe:C ratio of approximately 2:3. The paste wasagglomerated into pellets of approximately 3 millimetre diameter anddried until hard.

[0178] The dried pellets 501 were then evenly distributed across asinter strand type conveyor 502 configured to allow blast gases to passtherethrough.

[0179] The pellets 501 on the conveyor 502 were then passed through thereaction chamber 503 of the continuous conveyor fed reactor. Thereaction chamber 503 is configured with an inlet choke region 503 a ofrestricted cross section, an open main chamber region 503 b and anoutlet choke region 503 c of restricted cross-section. The dried pellets501 were first irradiated with microwave radiation via a preliminarywaveguide 504 in the inlet choke region 503 a at a frequency ofapproximately 915 MHz, providing preliminary heating of the pellets.This preliminary heating may bring the haematite/char reactants to above500° C., close to a temperature capable of initiating initial reductionreactions. As the heated pellets pass from the inlet choke region 503 atowards the main open region 503 b of the reaction chamber 503, they areirradiated with microwave radiation from central wave guides 505 at afrequency of 2450 MHz. In this central region, a hot air blast (atapproximately 800° C.) is imparted on the pelletised reactant chargefrom a blast inlet 506 positioned directly beneath the conveyor 502 inthe centre of the main chamber region 503 b. The hot oxygen of the airpassing through the carbon of the (now glowing red) hot reactants of theconveyor charge (at temperatures up to 1000° C.) rapidly converts tocarbon monoxide. An N₂/CO plasma is sustained immediately above thecharge in the region of the blast inlet 506, providing highly energeticreactive species in the primary reduction zone.

[0180] The reduction of haematite to elemental iron takes place througha series of reduction reactions which can be represented by Equations6(a) to 6(g) below (without ionisation equivalents), general systempressure and temperature, and with respect to the local ionisationenvironment of the plasma zone, the reaction path depending upon theavailable energy of activation and the reaction mechanism, whether asolid state or gas phase reaction.

1.5Fe₂O₃+0.5C

Fe₃O₄+0.5CO  6(a)

Fe₃O₄+C

3FeO+CO  6(b)

FeO+C

Fe+CO  6(c)

1.5Fe₂O₃+0.5CO

Fe₃O₄+0.5CO₂ 6(d)

Fe₃O₄+CO

3FeO+CO₂  6(e)

FeO+CO

Fe+CO₂  6(f)

CO₂+C

2CO  6(g)

[0181] Offtake gases produced from the reactions are exhausted throughthe exhaust outlet 507 and treated for heat recovery or blastregeneration.

[0182] The CO plasma is positionally maintained in the centre of thereaction chamber as a result of the location of the hot air blast inlet506 and the positioning of the main microwave radiation wave guides 505.The spongy solid reduced iron is subject to cooling as it travels fromthe plasma zone towards the outlet choke region 503 c. As the iron coolsbelow 950° C., nitrogen may be introduced to the atmosphere of theoutlet choke region 503 c to blanket the conveyor 502 and protect thereduced iron from re-oxidation which may result from free O₂ or from COwithin the cooling chamber environment being converted to CO₂ at thislower temperature regime at which CO₂ exhibits stability.

EXAMPLE 7

[0183] This example details another process to reduce haematite to ironutilising a rotary kiln device using the same basic preparation andchemistry as Example 6. The apparatus utilised to carry out the processof this example is depicted in FIG. 8.

[0184] Haematite/carbon pellets 601 prepared in accordance with Example6 were fed into the rotary kiln reaction chamber 603 via a reactantcharge inlet 602. The reaction chamber 603 was charged via gas inlet 606with a gas mixture of 10% CO in N₂ at low velocity, maintaining thepressure within the reaction chamber at approximately 1 atmosphere.

[0185] The 28 litre reaction chamber 603 was irradiated with microwaveradiation at a power of approximately 1000 watt and frequency of 2450MHz via a wave guide 605 positioned in a stationary end of the kiln,generating a CO/N₂ plasma throughout the central (16 to 20 litre) corevolume (not occupied by the revolving charge nor spiral ribs 609) of therotating reaction chamber 603.

[0186] The microwave radiation was moderated to prevent melting of thereactant charge, as detected and monitored by inspection of reductionproduct discharge which was drawn from the reaction chamber 603 via thedischarge outlet 608. Both solid and gaseous phase products of thereaction product were drawn from the discharge outlet 608.

EXAMPLE 8

[0187] This example details a process to reduce haematite (Fe₂O₃) to lowcarbon iron (Fe) product, using a principally solid state reductiontechnique of in-flight entrainment of fine particulate charge materialin a cyclone reactor. The apparatus utilised to carry out the process ofthis example is depicted in FIGS. 9(a) to 9(c).

[0188] Firstly haematite was prepared in a particulate form by millingto a grain size of less than 20 micrometres, and intimately blended withfine brown coal char milled to a grain size of less than 100micrometres.

[0189] The reactant blend of haematite/char was then entrained with ablast stream of air preheated to in excess of 400° C. through a cycloneinlet 701 located at the top of the cyclone reaction chamber 702. Theinlet 701 is arranged tangential to the cylindrical upper wall portionof the reaction chamber 702 such that the inlet blast air and entrainedcharged material follows a spiral path down through the reaction chamber702.

[0190] The blast air and entrained reactant charge were irradiated withmicrowave radiation at a frequency of 2450 MHz via a primary waveguide703 arranged to irradiate the air and reactant charge as it passed alongthe inlet 701 prior to entry into the reaction chamber 702 proper. Thepower of the microwave radiation applied was controlled to raise theblast air temperature to 1000° C. to ensure that free oxygen in theblast gases reacted with the fine char of the entrained charge blendconverting O₂ through carbon dioxide (CO₂) to carbon monoxide (CO). Theoperating pressure range was kept below the preferred pressure maximumof 300 kPa, such that the N₂/CO plasma formed beyond the port and in thecyclone reaction chamber was in the upper range of non-equilibriumconditions, raising the air to an appropriate temperature to ensure thatremaining free oxygen (O₂) and carbon dioxide (CO₂) in the blast airreacted with the fine char of the reactant charge blend to convert themto carbon monoxide (CO).

[0191] The reactant charge and blast air were further irradiated byfurther primary microwave waveguides 704 at the top of the reactionchamber 702, positioned around the circumference of the reaction chamber702 as indicated in FIG. 9(b).

[0192] Whilst the 2450 MHz frequency utilised in the present example wasfound to be effective and efficient in the present example, frequenciesin excess of 12 GHz were found to be preferable for this specificapplication.

[0193] In the non-equilibrium N₂/CO plasma environment toward the top ofthe reaction chamber, the haematite was reduced to magnetite, Fe3O4,utilising the highly energetic, reactive CO⁺ ions for primary reductionstimulation. The magnetite was subsequently reduced to the mostthermodynamically stable of the iron oxide phases, wustite, FeO, whichwas subsequently reduced to metallic iron. Any liquid phase formationfrom exothermic reactions was avoided by the in-flight cooling dynamicswithin the reaction chamber. The reduced product had the appearance ofsolid state reduction rather than re-solidification of a reduced liquidphase. Any tendency to CO₂ generation during the sequence of reductionwas countered by Boudouard gasification between remaining entrained charand CO₂ to re-generate CO (as per Equation 6(g)) in reaction chamber702.

[0194] This CO regeneration process was assisted through the addition offurther fine free carbon via the cyclone inlet 701. The CO produced fromthe CO₂ can be utilised for further reduction in the various stages ofthe haematite reduction to iron, and also provides protection againstoxidation of the elemental iron product.

[0195] The reactions of generating and re-generating CO are endothermic,and accordingly further external energy was required to maintain thetemperature within the reaction chamber. This energy was applied throughsupplementary microwave waveguides 705 positioned around thecircumference of the reaction chamber 702 and spaced therealong.

[0196] A typical circumferentially spaced pattern of supplementarywaveguides 705 is depicted in FIG. 9(c). The supplementary waveguides705 also provided the energy required for the final reduction stage ofthe FeO to metallic iron, which required considerably more is energythan the initial reduction stages.

[0197] The reduced iron particles cooled as the spiral path passed intothe lower tapered portion of the reaction chamber 702 below the effectof the various waveguides, and as a result of the mass of the ironparticles disengaged from the entrained flow and dropped into acollection chamber 706 at the base of the reaction chamber 702. Thecollection chamber was blanketed with CO (or alternately inert gas) toprotect the reduced iron from oxidation. The solid iron productretrieved from the collection chamber 706 was in the form of high carbonsteel powder, which was relatively low in carbon (0.3 wt % to 1 wt %compared to iron).

[0198] Off-take gases from the various reactions were extracted from theexhaust gas outlet 707 located in the centre of the top of the reactionchamber 702, and diverted to appropriate gas handling systems (baghouse,scrubbing, gas regeneration as appropriate).

[0199] The off-take gases primarily consisted of N₂, CO and CO₂.

[0200] The person skilled in the art will appreciate the manner in whichthe various forms of reaction can be applied utilising the radiationstimulated plasma of the present invention.

1. A process for the reduction of a metalliferous ore or concentratecomprising the steps of: preparing said ore or concentrate into aparticulate form; charging a reaction chamber with said ore orconcentrate, a reductant and an input gas; irradiating said reactionchamber with electromagnetic radiation within a frequency range of 30MHz to 300 GHz until a non-equilibrium plasma is initiated, andsustaining and controlling said non-equilibrium plasma with saidradiation until said ore or concentrate is reduced to form reductionproduct.
 2. The process of claim 1 wherein pressure within said reactionchamber is maintained below 300 kPa during irradiation thereof.
 3. Theprocess of claim 2 wherein said pressure is also maintained above is 40kPa.
 4. The process of claim 3 wherein said pressure is maintained atabout atmospheric pressure.
 5. The process of claim 1 wherein saidplasma is initiated in said input gas.
 6. The process of claim 1 whereinat least part of said input gas is decomposed during said irradiation,said plasma being initiated at least in part in the decomposed productof said input gas.
 7. The process of claim 1 wherein said reductantcomprises a carbonaceous material.
 8. The process of claim 7 whereinsaid reductant includes a particulate carbonaceous material blended withsaid ore or concentrate.
 9. The process of claim 7 wherein saidreductant includes carbon monoxide gas, said input gas including saidcarbon monoxide gas, said plasma being initiated ate least in part insaid carbon monoxide gas.
 10. The process of claim 7 wherein saidreductant comprises carbon monoxide gas and a particulate carbonaceousmaterial.
 11. The process of claim 1 wherein said reductant comprises areactive metal.
 12. The process of claim 1 wherein said input gasincludes an inert gas.
 13. The process of claim 1 wherein said inert gascomprises argon or nitrogen.
 14. The process of claim 1 wherein saidinput gas comprises air.
 15. The process of claim 7 wherein saidreductant includes methane.
 16. The process of claim 1 wherein saidradiation is microwave radiation.
 17. The process of claim 1 whereinsaid ore or concentrate is a concentrate derived directly from minedore.
 18. The process of claim 1 wherein said ore or concentrate is anon-ore derived concentrate.
 19. The process of claim 1 wherein said oreor concentrate is a concentrate in the form of a residue derived frommetallurgical processing operations.
 20. The process of claim 1 whereinsaid reaction chamber is in the form of a fluidised bed reactor.
 21. Theprocess of claim 1 wherein said reaction chamber is in the form of anoven, said ore or concentrate being charged into a crucible placedwithin said oven.
 22. The process of claim 1 wherein said reactionchamber is in the form of a rotary kiln reactor.
 23. The process ofclaim 1 wherein said reaction chamber is in the form of a cyclonereactor.
 24. The process of claim 1 wherein said reaction chamber is inthe form of a conveyor fed reaction.
 25. The process of claim 24 whereinsaid ore or concentrate is prepared into a pelletised particulate form.26. The process of claim 1 wherein said reduction product is of metallicform.
 27. The process of claim 26 wherein said metallic reaction productis in the from of a fume, said fume being extracted from said reactionchamber and separated from gases produced during said reduction.
 28. Theprocess of claim 1 wherein said reduction product is a compound ofreduced oxidation state.
 29. The process of claim 1 wherein saidreduction product is formed by reduction of said ore or concentratethrough a series of subsequent reduction reactions.
 30. The process ofclaim 1 wherein said process includes the step of generating carbonmonoxide, said plasma being initiated and sustained at least in part insaid carbon monoxide.
 31. The process of claim 30 wherein said input gasincludes air, said reductant includes particulate carbonaceous materialand said carbon monoxide is generated from reaction of oxygen withinsaid air with said particulate carbonaceous material.
 32. The process ofclaim 30 wherein said reductant includes particulate carbonaceousmaterial and said carbon monoxide is generated from reaction of carbondioxide produced during said reduction with said particulatecarbonaceous material.
 33. The process of claim 30 wherein particulatecarbonaceous material is introduced into said reaction chamber afterinitiation of said plasma, said carbon monoxide being generated fromreaction of carbon dioxide produced during said reduction, with saidintroduced particulate carbonaceous material.
 34. The process of claim30 wherein said input gas includes air and particulate carbonaceousmaterial is introduced into said reaction chamber after initiation ofsaid plasma, said carbon monoxide being generated from reaction ofoxygen within said air with said introduced particulate carbonaceousmaterial.
 35. The process of claim 1 wherein said ore or concentrate isenveloped in a non-oxidising or inert gas environment during saidreduction and during cooling of said reduction product followingirradiation of said reaction chamber.
 36. The process of claim 35wherein said non-oxidising or inert gas is introduced to said reactionchamber during said cooling.
 37. The process of claim 1 wherein saidinput gas is passed through said ore or concentrate during saidirradiating step.
 38. The process of claim 37 wherein said input gas isblasted upwardly through said ore or concentrate.
 39. The process ofclaim 1 wherein said input gas is preheated prior to charging into saidreaction chamber.